Sir Guy Grand adopts homeless bum Youngman to be heir to his obscene wealth, and immediately begins bringing him into the intricacies of the family business, which is to prey upon people's greed by use of the vast holdings of the Grand empire. They leave no stone unturned as sporting events, restaurants, art galleries, and traditional pheasant hunts turn into lurid displays of bad manners and profiteering. Things climax at the social event of the season, the inaugural voyage of the new pleasure cruiser The Magic Christian.

John Cleese is hilarious as the descendant of Sherlock Holmes in this modern detective drama of international power politics and intrigue. Unlike his illustrious grandfather however, he only succeeds in bungling every job he organizes. Also stars Arthur Lowe as the "bionic" grandson of Dr. Watson, Stratford Johns as the Commissioner of Police, and Connie Booth as Mrs. Hudson.